- Load hits produced on the hitmaker step.
- Load alignment constants :
- Apply the planes' shifts obtained on the pre-alignment step (a part of the hitmaker step) to correct the hits' positions;
- Consecutively apply the planes' shifts obtained on the previous alignment step(s) to correct the hits' positions, i.e. on the alignment step
, apply**n**sets of the planes' shifts obtained during previous**n-1**alignment steps.**n-1**

- Form track(s) out of the hits corrected on the step 2 :
- Make two groups of hits; each group consists of three hits corresponding to the planes of each telescope arm, i.e. three hits found on the upstream telescope arm (
) and three hits on the downstream arm (*triplet*);*d**riplet* - Combine triplet(s) and driplet(s) to
**track(s)**

- Make two groups of hits; each group consists of three hits corresponding to the planes of each telescope arm, i.e. three hits found on the upstream telescope arm (
- Create the GBL
out of the formed tracks**trajectory(ies)** - Pass the created GBL trajectory(ies) to
*Millepede-II*for a fine alignment of the (telescope) planes. - Write the shift constants obtained by Millepede-II per each plane of interest to an *.
*slcio*file.

Steps 3-6 of the algorithm above are being processed by the **EUTelMilleGBL.cc** code.

# Histograms description

A resulting *.root file after performing the align step has the following structure:

**Proj_to_Plane0**: folder is contained by the \mathrm{x_{i}\,-\,x_{0}\,and\,y_{i}\,-\,y_{0}} distr., whereis the plane number;*i***Triplets**: contains three sub-folders (**Upstream**and**_arm****Downstream**folders have the same structure)**_arm****Upstream_arm**:**Downstream****_arm**:**StraightLine_tracks**:

**GBLtrajectories**

# Results

## Comparison of the results depending on the number of align steps

Fig. 1.1. X residual distributions between the tel. plane hits and the GBL trajectory. | Fig. 1.2. The Mean value and Sigma distr. of the residual distr. Gaussian fit per tel. plane. |
---|

* Fig 1.1, 1.2* show the X residual and their fits' parameters distr. per each tel. plane after different alignment step. Each alignment step was performed with the following cuts:

triCut = 60, driCut = 80, sixCut = 150, TelescopeResolution = 10.

Residual distr. "spread" doesn't decrease with additional alignment step(s), while the mean value is being fixed to ~0 after the first alignment step. The residual distr. spread rises up by a factor of ~10-15 due to the scattering at DUT (DUT material budged was estimated to be equal to * 0.265*, DUT inclination angle is 0 deg., in the units of rad length).

Fig. 2.1. X residual distributions between the tel. plane hits and the GBL trajectory. | Fig. 2.2. The Mean value and Sigma distr. of the residual distr. Gaussian fit per tel. plane. |
---|

* Fig. 2.1, 2.2* show the X residual distr. and their fits' mean and sigma values after diff. align steps, the cuts which were used:

step 1: triCut = 60, driCut = 80, sixCut = 150, TelescopeResolution = 10; step 2,3 : triCut = 15, driCut = 20, sixCut = 20, TelescopeResolution = 4.

Step 2 gives a slight improvement for the residual distr. spread, while the step 3 makes the mean and spread worse for the downstream telescope arm's planes.

# Presentations and scripts